The present invention relates generally to plasma-based thin film processing. More particularly, the invention relates to an arc control apparatus for DC sputtering systems that decreases the recovery time from an arc.
With the increasing demand for optical and disk media such as CD, DVD, MD, MO, DLC films, and hard disks; the importance of the sputtering processes that are used in the manufacture of these media continues to increase. There are numerous types of sputtering systems, all of which are employed to deposit insulating or conductive coatings on devices ranging from semiconductors to drill bits. The films that are generally applied to optical and disk media are typically created with a sputtering process having poor control over the sputtering gas, i.e. a significant fraction of atmosphere and petrochemical volatilities are in the chamber at the beginning of the process.
During the initial sputtering phase, atmosphere is introduced into the plasma chamber to combine with freed target material. The resulting compound, typically oxides and nitrides, may form a film on the surface of the target. This is referred to as target poisoning, and will cause arcing in DC sputtering. Arcing, though inevitable in these processes is a mixed blessing. The arc often removes the poisoning from the target, but it may also generate undesirable particles to damage the substrate or disk.
Further sources of arcing include contaminants such as moisture, atmospheric gases, inclusions, and outgassing from the workpiece may also cause arcing.
In addition to particulate defects, arcing may lead to a defect commonly known as “mousebites”, which is illustrated in FIG. 1. A mousebite 9 is an irregularity that generally occurs along the edges of a workpiece coating. The occurrence of mousebites is related to the configuration of the power supply and attached energy storage components. In applications such as coating CDs, the effect of mousebites can be attenuated by increasing the portion of the workpiece adjacent to the edges that is masked from coating. However, masking limits the usable area of the workpiece, thereby increasing the need for maintenance, i.e. replacement of the mask due to coating buildup.
To control arcs, conventional DC sputtering systems include arc suppression systems that are either attached to or integrated into the power supply. Arc suppression systems may be divided into two groups. The first type, periodic arc control systems, cause a periodically occurring interruption or voltage reversal of the cathode voltage in an attempt to avoid arcing. The second type, arc initiated control systems, bring about an interruption only after the beginning of an arc has been detected.
Periodic suppression systems universally employ at least one active switch (in shunt or series to the cathode) to interrupt the flow of current or to apply a reverse voltage to the cathode. The frequency and pulse width of the switch are normally set so that arcing is suppressed, thereby eliminating defects that result from target poisoning and its associated arcs. A disadvantage of periodically interrupting the cathode voltage is that the basic deposition rate may be reduced since the cathode voltage is not continuously applied. Another disadvantage of periodic suppression systems is the additional cost of the active devices and associated control circuits. Generally, periodic suppression systems are only employed when defect free deposition is required, such as in the manufacture of semiconductors.
Arc initiated control is employed for the manufacture of devices in which lower cost and reduced deposition times are the primary requirements. Traditionally, an arc initiated control system senses the initiation of an arc, and in response disables the power supply driving the cathode. Generally, these control systems permit a significant quantity of energy to be dissipated in the arc before disabling the power applied to the cathode. The quantity of energy dissipated in the arc is also dependent on the type of power supply to which the arc initiated control system is attached. Since arc control systems do not completely prevent arcing like periodic suppression systems, but instead act in response to the detection of an arc, particulate defects to varying degrees will occur. In addition, with some combinations of power supplies and arc initiated control systems, mousebite defects may also occur. In addition, deposition times may also be adversely affected, since while an arc occurs there is no deposition on the substrate.
While the prior art can be used to provide a DC sputtering system, it has not proven capable of providing low cost arc control that does not adversely affect the deposition time or the quality of the coating. Accordingly, it is desirable to provide a low defect arc control system that does not compromise the deposition rate of the process. In addition, eliminating defects from the workpiece is desirable. Also, it is desirable to reduce deposition defects caused by target poisoning.
The present arc control system and method provide a system for controlling an arc. The arc control system includes a sputtering chamber that houses an anode and a sputtering target formed from a target material and serving as a cathode. A DC power supply provides a DC cathode voltage such that a cathode current flows from the anode to the cathode. A resonant network is coupled between the DC power supply and the chamber. The resonant network has sufficient Q so that in reaction to the occurrence of an arc, the cathode current resonates to a negative value as is well known in the art. A reverse voltage clamp is coupled across the resonant network to clamp the cathode voltage to a predetermined reverse voltage value, and allow the negative portion of the resonant waveform to drive the cathode and reverse charge the target surface. Thus reverse current of the network is allowed to flow unimpeded to the cathode. This reverse current then charges the cathode to a clamped positive voltage.
For a more complete understanding of the invention, its objects and advantages, reference may be had to the following specification and to the accompanying drawings.